--- module: 055-02 language: en chapter: 55 title: "The Eye: Visual Physiology, Examination, and Common Disease" module_title: "Visual localisation, sight-threatening emergencies, and systemic ocular disease" source_sha256: ae6440942477451a897042822eab185acc4d7b3cf61743caef0a77e323afc239 --- # Localisation, emergencies, and systemic disease ## Localising visual failure ### Failed step: optics, receptors, nerve, alignment, cortex ### Monocular loss: eye or anterior pathway ### Homonymous loss: behind the chiasm ### Binocular diplopia resolves with cover: misalignment ## Acuity and examination ### Acuity first, each eye, usual correction #### Drops, pressure, pain can change it ### Record counting fingers to light projection ### Baseline and change set urgency ### Unseen disc recorded as not visualised #### Leads to dilated examination or imaging ## Phototransduction and retinal processing ### Light alters chromophore, activates opsin cascade #### Cyclic nucleotide falls, cell hyperpolarises #### Darkness gives tonic glutamate release ### ON and OFF bipolars code increments, decrements ### Ganglion output is processed, not a pixel copy ### Fovea trades convergence for acuity ## Pupils and visual fields ### Light reflex: afferent to midbrain, third-nerve efferent ### Relative afferent defect #### Light to worse eye: both pupils dilate #### Asymmetric retina or nerve, cannot tell which ### Anisocoria worse in light: larger pupil fails ### Anisocoria worse in dark: smaller pupil fails ### Chiasmal compression: temporal fields ### Tract to cortex: contralateral homonymous loss ### Temporal radiations upper, parietal lower fields ## Red eye and orbit ### Keratitis: staining, opacity, severe pain #### Urgent cultures, intensive organism-directed drops #### Patching or casual steroid speeds destruction ### Anterior uveitis: ciliary injection, small pupil, cells #### Steroid and cycloplegia after ophthalmic check ### Scleritis: boring pain waking sleep, vasculitis ### Orbital cellulitis: fever, proptosis, painful movement #### Watch nerve compression, sinus thrombosis #### Imaging, intravenous antibiotics, joint care ## Angle closure, chemicals, and trauma ### Angle closure: aqueous cannot reach meshwork #### Pain, halos, nausea, haze, mid-dilated pupil #### Laser relieves pupillary block #### Nausea must not suggest a gut diagnosis ### Chemical injury treated before history #### Irrigate until pH stays neutral #### Alkali saponifies and penetrates rapidly ### Penetrating trauma: rigid shield, no pressure #### Avoid tonometry, and magnetic resonance if metal ## Sudden painless loss and arteritis ### Arterial occlusion cuts inner-retinal perfusion #### Carotid or cardiac emboli, arteritis ### Transient monocular dimming is retinal ischaemia #### Serious even when examination normalises ### Venous occlusion: haemorrhage and oedema #### Signals pressure, diabetes, glaucoma, thrombosis ### Giant-cell arteritis infarcts the optic nerve #### Headache, scalp tenderness, jaw claudication #### Inflammatory markers occasionally normal #### Immediate high-dose steroid ##### Fellow eye can go blind within days ## Retina, optic nerve, and diplopia ### Flashes: vitreous traction stimulates retina ### Sudden floaters or curtain: urgent dilated exam ### Macula-on detachment exceptionally urgent ### Optic neuritis: subacute, colour loss, painful #### Disc normal if inflammation posterior ### Ischaemic optic neuropathy: sudden, altitudinal ### Diplopia localised by position, lid, pupil #### Pupil-involving third palsy: aneurysm #### Internuclear ophthalmoplegia: medial fasciculus #### Fatigable ptosis: neuromuscular junction ## Glaucoma, diabetes, macula, and children ### Glaucoma is ganglion-cell and axon loss #### Progression at normal pressure occurs #### Pressure is the only modifiable factor #### Punctal occlusion cuts systemic absorption ### Diabetes: leakage, closure, ischaemia, growth factor #### Neovascularisation: bleeding, traction, glaucoma #### Rapid correction may transiently worsen ### Macular degeneration spares peripheral navigation #### New distortion needs rapid retinal therapy ### Child red reflex, leukocoria, strabismus: urgent ## Systemic window and discharge ### Papilloedema: raised intracranial pressure ### Safe habit: acuity, pattern, treat tissue first ### State driving and hazardous work limits ### Return signs: vision loss, pain, curtain ### Drops: name, eye, frequency, duration